Multiple independent nested stent structures and methods for their preparation and deployment

ABSTRACT

Blood vessels and other body lumens are stented using stent structures comprising a plurality of radially expansible rings where at least some of the rings comprise axially extending elements which interleave with axially extending elements on adjacent unconnected rings. The ring structures may be open cell structures or closed cell structures, and the axially extending elements will typically be formed as part of the open cell or closed cell structure.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of U.S. ProvisionalPatent Application No. 60/440,839 (Attorney Docket No. 21629-000500US),filed Jan. 17, 2003, entitled “Multiple Independent Nested StentStructures & Methods for Their Deployment,” which application is herebyincorporated fully by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to medical devices andmethods. More particularly, the present invention relates to apparatusand methods for delivering a plurality of separate luminal prostheseswithin a body lumen, such as a blood vessel.

[0004] Coronary artery disease is the leading cause of death andmorbidity in the United States and Western society. In particular,atherosclerosis in the coronary arteries can cause myocardialinfarction, commonly referred to as a heart attack, which can beimmediately fatal or, even if survived, can cause damage to the heartwhich can incapacitate the patient.

[0005] While coronary artery bypass surgery can be an effectivetreatment for stenosed arteries resulting from atherosclerosis or othercauses, it is a highly invasive procedure which is also expensive andwhich requires substantial hospital and recovery time. Percutaneoustransluminal angioplasty, commonly referred to as balloon angioplasty,is less invasive, less traumatic, and significantly less expensive thanbypass surgery. Heretofore, however, balloon angioplasty has not beenconsidered as effective a treatment as bypass surgery. The effectivenessof balloon angioplasty, however, has improved significantly with theintroduction of stenting, which involves the placement of a scaffoldstructure within an artery that has been treated by balloon angioplasty.The stent inhibits abrupt reclosure of the artery and has some benefitin inhibiting subsequent restenosis resulting from hyperplasia.

[0006] Presently available stents may be generally categorized as either“closed cell configurations” or “open cell configurations.” Closed cellconfigurations are characterized by ellipses, ovals, and polygonalstructures, such as closed boxes, rhomboids, diamonds, and the like,which open in the circumferential direction and shorten in the axialdirection as the stent is expanded. Open cell configurations includezigzag and serpentine structures which may be formed as a plurality ofdiscreet rings or may be formed from a single continuous wire or otherelement. Closed cell stents are advantageous in that they provide bettercoverage of the blood vessel wall when the stent is deployed. This isparticularly advantageous in tightly curved segments of the vasculaturewhere even stent coverage in both the axial and circumferentialdirections on the outer wall of the vessel has been shown to reducerestenosis. Such even coverage is also an advantage in achieving uniformdelivery from drug eluting stents. In contrast, open cell stentconfigurations are generally more flexible than the closed cellconfigurations. Such flexibility is advantageous in the tortuous regionsof the vasculature where enhanced flexibility can provide betterconformance to the vessel being treated. Better conformance can reducethe stress on the vessel wall, particularly at the stent ends, and leadto reduced restenosis.

[0007] For these reasons, it would be desirable to provide improvedstents and stent structures. In particular, it would be desirable toprovide stents and stent structures which combine the improved wallcoverage of closed cell stent structures with the increased flexibilityof open cell stent structures. It would be still further desirable ifsuch improved stent structures allowed a physician to optimize thelength of vessel being treated in accordance with the nature of thedisease, allowed for the delivery of both very short and very long stentstructures, and optionally permited delivery of stent structures atmultiple contiguous and/or non-contiguous locations within a body lumen.At least some of these objectives will be met by the inventionsdescribed hereinafter.

[0008] 2. Description of the Background Art

[0009] U.S. Pat. Nos. 6,200,337 and 5,870,381 describe stents havingclosed cell rings with overlapping portions connected by axialconnecting members. U.S. Pat. No. 6,375,676 describes a stent havingopen cell rings with overlapping portions connected by axial connectingmembers. U.S. Patent Application Publication Nos. 2002/0188343 and2002/0188347 describe expandable stents having interconnecting elementswhich interlock circumferentially adjacent bridges between axiallyadjacent stent segments. U.S. Pat. No. 4,580,568 describes thesequential placement of a plurality of zigzag ring stents where thestents may optionally be overlapped (FIGS. 7 and 8). U.S. Pat. No.6,319,277 describes a stent formed from a single element into aplurality of nested “waves.” U.S. Pat. No. 5,554,181 describes a stentformed from a single element into partially overlapping windings. Otherpatents of interest include U.S. Pat. Nos. 6,312,458; 5,879,370;5,755,776; 5,507,771; and 5,104,404. U.S. Pat. No. 6,258,117 BIdescribes a stent having multiple sections connected by separable orfrangible connecting regions. Optionally, the connecting regions aresevered after the stent structure has been implanted in the bloodvessel. U.S. Pat. Nos. 5,571,086; 5,776,141, and 6,143,016 describe anexpandable sleeve for placement over a balloon catheter for the deliveryof one or two stent structures to the vasculature. U.S. Pat. No.5,697,948, describes a catheter for delivering stents covered by asheath.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention provides methods and apparatus forprosthesis placement, such as stenting of body lumens, typically bloodvessels, and more typically coronary arteries. The methods and systemswill also find significant use in the peripheral vasculature, thecerebral vasculature, and in other ducts, such as the biliary duct, thefallopian tubes, and the like. The terms “stent” and “stenting” aredefined to include any of the wide variety of expandable prostheses andscaffolds which are designed to be intraluminally introduced to atreatment site and expanded in situ to apply a radially outward forceagainst the inner wall of the body lumen at that site. The stents andprostheses of the present invention commonly comprise a closed or, lesspreferably, an open lattice structure, and are typically formed from amalleable or elastic metal. When formed from a malleable metal, such asstainless steel, gold, platinum, titanium, and super alloys, the stentswill typically be expanded by a balloon which causes plastic deformationof the lattice so that it remains opened after deployment. When formedfrom an elastic metal, including super elastic metals such asnickel-titanium alloys, the lattice structures will usually be radiallyconstrained when delivered and deployed by releasing the structures fromsuch radial constraint so that they “self-expand” at the target site.When the stent or lattice structures are covered with a fabric orpolymeric membrane covering, they are commonly referred to as grafts.Grafts may be used for the treatment of aneurysms or other conditionswhich require placement of a non-permeable or semi-permeable barrier atthe treatment site. The terms “stent” and “stent structures” referbroadly to all radially expansible stents, grafts, and otherscaffold-like structures which are intended for deployment within bodylumens.

[0011] The stents and stent structures of the present invention may haveany of a variety of common constructions, including closed cellconstructions such as expansible ovals, ellipses, box structures,expandable diamond structures, expandable rhomboid structures, as wellas other regular and irregular polygonal structures, etc. In addition,the closed cells may have complex slotted geometries, such as H-shapedslots, I-shaped slots, J-shaped slots, etc. Suitable open cellstructures include zigzag structures, serpentine structures, and thelike. Such conventional stent structures are well described in thepatent and medical literature. Specific examples of suitable stentstructures are described in the following U.S. Patents, the fulldisclosures of which are incorporated herein by reference: U.S. Pat.Nos. 6,315,794; 5,980,552; 5,836,964; 5,527,354; 5,421,955; 4,886,062;and 4,776,337. Preferred structures are described herein with referenceto FIGS. 4 and 5.

[0012] According to one aspect of the present invention, stents willcomprise a plurality of independent expansible rings each having alength of 1 mm or greater, usually 2 mm or greater, and sometimes of 3mm or greater, usually being in the range from 1 mm to 10 mm, typicallyfrom 2 mm to 7 mm, more typically from 2 mm to 5 mm. The use of suchshort ring lengths is advantageous since the overall stent length willbe a multiple of the ring length.

[0013] The methods and apparatus of the present invention will providefor the deployment of a plurality of stents or other prostheses from acommon stent delivery catheter. Usually, the number of delivered stentswill be in the range from 2 to 50, typically from 3 to 30, and mosttypically from 3 to 25. As more stents are placed on the deliverycatheter, the individual stent length will often be somewhat less,although this is not necessarily the case in all instances. The multipleprostheses may be deployed individually or in groups of two or more at asingle location or at multiple spaced-apart locations in the body lumenor lumens.

[0014] In another aspect of the present invention, stent structures willcomprise a plurality of radially expansible rings, as generallydescribed above, arranged along an axial line. Expansible rings arearranged adjacent to each other and will include axially extendingelements which interleave or nest with similarly axially extendingelements on adjacent rings. By “interleaved” it is meant that theaxially extending elements on adjacent rings will interpenetrate witheach other in an axial direction, at least prior to stent expansion andpreferably even after stent expansion. Usually, the interpenetratingelements will not overlap, i.e., be positioned one over another in theradial direction, but it is possible that in some implementations theremay be some overlapping prior to or even after expansion. The axialinterpenetration will be at least 0.1 mm, usually being at least 1 mm,and often being in the range from 1 mm to 5 mm, and will of coursedepend on the axial length(s) of the adjacent ring(s). Expressed as apercentage, the axial length of the axially extending elements willusually be at least 5% of the axial length of the ring, usually beingfrom 5% to 50%, and preferably being from 20% to 30%.

[0015] Preferably, the axially extending elements on adjacent rings willinterleave without interlocking so as to permit axial separation betweenthe adjacent rings prior to expansion of the rings. However, axiallyextending elements may, in some instances, also interpenetrate in aperipheral direction prior to expansion. Such peripheralinterpenetration can provide axial interlocking of the axially adjacentexpansible rings prior to expansion. It will usually be desirable oreven necessary that the peripheral interpenetration be relieved duringradial expansion of the stent structures so that the independent ringsbe released from each other when deployed. In other instances, however,a tether or other types of links may be provided to interconnect orotherwise restrain the rings even after expansion and deployment.

[0016] It is not necessary that all adjacent rings be unconnected,although at least two, and preferably three, four, five, eight, ten, ormore adjacent rings will be unconnected. Thus, some (but fewer than all)of the adjacent rings of the stent structures may have ties or linkstherebetween, including flexible or non-flexible (deflectable) ties orlinks. The axially adjacent rings, however, will usually not beconnected, although in some cases they may have easily separable ornon-permanent connections as described in more detail below. Eachexpansible ring will preferably comprise expansible closed cellstructures, as set forth above. Less preferably, the expansible ringsmay comprise expansible open cell structures, as set forth above. Thelengths and diameters of the individual rings have been set forthgenerally above. The stent structure will typically comprise from 2 to50 individual rings, usually from 3 to 30 individual rings, and oftenfrom 3 to 25 individual rings.

[0017] The spacing between adjacent rings may be uniform or non-uniform,preferably being uniform. In some cases, it is desirable that the edgesof the adjacent rings be spaced-apart by a uniform distance in the axialdirection, typically at least 0.1 mm, usually being from 0.1 mm to 0.5mm, prior to stent expansion. In other situations, it will be preferredthat the adjacent rings be in contact with each other at discreet pointsor along continuous sections of the edges. In some cases, the stentstructures will be configured to shorten upon expansion to increase thespacing between rings. It is usually preferable that the edges of theadjacent rings not overlap, at least prior to deployment. Deployment ofthe stents, particularly in curved and tortuous luminal regions, maysometimes result in touching and overlapping of the stent rings.

[0018] The stent structures may be modified in a variety of ways whichare used with other conventional stents. For example, some or all of theradially expansible rings may releasably carry a biologically activeagent, such as an agent which inhibits hyperplasia. Exemplaryanti-hyperplasia agents include anti-neoplastic drugs, such aspaclitaxel, methotrexate, and batimastal; antibiotics such asdoxycycline, tetracycline, rapamycin, everolimus and other analogs andderivatives of rapamycin, and actinomycin; amino suppressants such asdexamethasone and methyl prednisolone; nitric oxide sources such asnitroprussides; estrogen; estradiols; and the like.

[0019] In another aspect of the present invention, a stent deploymentsystem comprises an elongate carrier having a central axis and includinga plurality of radially expansible rings arranged over a surfacethereof. At least some of the radially expansible rings will have thefeatures and characteristics just described with respect to the presentinvention. The elongate carriers of the stent deployment systems willtypically comprise a radially expansible balloon having an outer surfacewhere the radially expansible rings are disposed over the outer surfaceof the balloon. In such cases, the balloon may comprise a singleinflation chamber in which case all of the rings will be expandedsimultaneously. Alternatively, the balloon may comprise a plurality ofindependently inflatable chambers so that individual expansible ringsmay be deployed separately from the other rings.

[0020] The elongated carrier of the stent deployment system mayalternatively comprise a carrier tube having an inner surface whichcarries and constrains the radially expansible rings. In such cases, theexpansible rings will usually be self-expanding, i.e., held in aradially constrained configuration by the carrier tube prior to releaseand expansion at a luminal target site. Usually, the carrier tubestructures will further comprise a pusher tube arranged to axiallyadvance the radially expansible rings from the carrier tube. Theelongated carrier may still further comprise a balloon arranged toreceive and expand individual rings as they advance from the carriertube, in which case the carrier may be used for delivering the formable(balloon-expansible) stent structures. However, such a balloon may alsobe used with self-expanding stent structures to control or enhanceexpansion, to perform predilatation of a lesion prior to stentdeployment, or to further expand the stent structures and dilate thevessel lumen after the structures have self-expanded.

[0021] In a further aspect of the present invention, multipleindependent stent rings are arranged on a carrier by the followingmethods. An elongated carrier structure is provided and a plurality ofradially expansible rings comprising axially extending elements aremounted on the carrier structure such that the axially extendingelements on adjacent rings interleave or nest after they are mounted.The number of rings mounted on the carrier is selected to provide adesired overall stent length, and the number of rings is typically inthe ranges set forth above, providing overall stent lengths in the rangefrom 6 mm to 120 mm, usually from 9 mm to 100 mm, and typically from 12mm to 50 mm. Other aspects of the individual radially expansible ringshave been described above.

[0022] In yet another aspect of the present invention, methods forstenting a body lumen comprise delivering to the body lumen a stentstructure having a plurality of radially expansible rings. The rings areas described above with respect to other aspects of the presentinvention, and at least some of the rings are expanded within the bodylumen so that the axially extending elements open and axially move apartfrom each other as they radially expand. Preferably, the length of theaxially extending elements and degree of radial expansion will beselected so that the elements remain interleaved even after being fullyexpanded within the body lumen. Such an interleaving structure enhancesthe continuity of lumenal wall coverage provided by the deployed stentstructure. Target body lumens are typically blood vessels, moretypically arteries, such as coronary arteries. The rings may bedelivered simultaneously, typically using a single inflatable balloon,or sequentially, typically using a carrier tube, pusher tube andoptionally deployment balloon. Methods may be used for delivering from 3to 50 rings, usually from 3 to 30 rings, and typically from 3 to 25rings, to cover a luminal length in the range from 6 mm to 120 mm,usually from 9 mm to 100 mm, and typically from 12 mm to 50 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a schematic illustration of a stent structure accordingto the present invention comprising a plurality of closed cell ringstructures.

[0024]FIG. 2 illustrates the stent structure of FIG. 1 shown in itsradially expanded configuration.

[0025]FIGS. 2A and 2B illustrate the difference in deployedconfiguration of non-nested and nested stent structures, respectively.

[0026]FIG. 3 illustrates a stent structure constructed in accordancewith the principles of the present invention comprising a plurality ofopen cell expansible rings.

[0027]FIG. 4 illustrates the stent structure of FIG. 3 shown in itsradially expanded configuration.

[0028]FIG. 5 illustrates a first exemplary expansible ring structure inaccordance with the principles of the invention.

[0029]FIG. 6 illustrates a stent structure comprising a plurality of thering structures of FIG. 5, shown in a rolled out radially collapsedconfiguration.

[0030]FIGS. 6A and 6B illustrate variations on the ring structure ofFIG. 6, where the variations are chosen to inhibit axial separation ofthe ring structures prior to deployment.

[0031]FIG. 7 illustrates the stent structure of FIG. 6 shown in itsradially expanded configuration.

[0032]FIG. 8 illustrates a second exemplary expansible ring structure inaccordance with the principles of the present invention.

[0033]FIG. 9 illustrates a stent structure comprising a plurality of therings of FIG. 8.

[0034]FIG. 10 illustrates the stent structure of FIG. 8 in its radiallyexpanded configuration.

[0035]FIGS. 11-14 illustrate further exemplary expansible ringstructures in accordance with the principles of the present invention.

[0036]FIGS. 15A and 15B illustrate a further embodiment of a stentstructure according to the present invention shown in unexpanded andexpanded configurations, respectively.

[0037]FIGS. 16A and 16B illustrate a still further embodiment of a stentstructure according to the present invention shown in unexpanded andexpanded configurations, respectively.

[0038]FIGS. 17A and 17B illustrate deployment of a closed cell stentstructure according to the present invention with both a balloon havinga single chamber (FIG. 16) and a balloon having multiple chambers topermit selective delivery of portions of the stent structure (FIG. 17).

[0039]FIGS. 18A-18D illustrate deployment of a plurality of a expansiblerings which form a stent structure according to the present inventionusing a delivery tube and pusher tube in combination with an expansionballoon.

[0040]FIG. 19 illustrates a kit constructed in accordance with theprinciples of the present invention.

[0041]FIGS. 20A-20B, 21A-21B, and 22A-22B illustrate further embodimentsof stent structures according to the invention in unexpanded andexpanded configurations.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention provides apparatus, systems, and methodsfor preparing and delivering stent structures comprising a plurality of“separate” or “discreet” radially expansible ring segments. By“separate” or “discreet,” it is meant that the ring segments areunconnected (or easily disconnected) at the time they are delivered to atarget body lumen. Usually, the ring segments will be closely packed toprovide a relatively high degree of vessel wall coverage after they areexpanded. By disconnecting the adjacent segments, however, such atightly packed structured can retain a very high degree of flexibilitypermitting delivery and conformance in even highly torturous regions ofthe vasculature and other body lumens.

[0043] The ability to closely pack the expansible ring segments andachieve a high degree of vessel wall coverage is achieved at leastpartly because at least some of the axially adjacent rings compriseaxially extending elements which interleave or nest with axiallyextending elements on an adjacent connected ring. Usually, the axiallyextending elements will be formed from a radially expansible portion ofthe ring, e.g., the element will be part of the closed cell structure oropen cell structure as described in more detail hereinbelow. As theseexpansible sections will typically foreshorten as they are radiallyexpanded, interleaving and nesting the segments on adjacent rings priorto expansion minimizes or preferably eliminates any gaps in coverageafter the stent is expanded, as described in more detail below.

[0044] The stent structures of the present invention may be fabricatedas either balloon-expansible or self-expanding stents according tomethods well known in the art. Typical deformable materials suitable forfabricating balloon-expansible stent structures include 316L stainlesssteel, gold, platinum, cobalt chrome, platinum, and the like. Suitableresilient materials for self-expanding stents include nickel titaniumalloys, various spring stainless steel alloys, Eligloy® alloy, and thelike. It will also be possible to form the stent structures of thepresent invention from both natural and synthetic polymers. Naturalpolymers include collagen, gelatin, chitin, cellulose, and the like.Suitable synthetic polymers include polyglycolic acids (PGA), polylacticacids (PLA), poly ethylene glycols (PEG), polyamides, polyimides,polyesters, and the like. In some instances, it would be possible toform different radially expansible segments from different materials inorder to achieve different properties.

[0045] The stent structures will comprise a plurality of the individualradially expansible ring segments with typical dimensions, numbers, andthe like, described above in the summary. The plurality of ring segmentswill be arranged prior to delivery, in a manner suitable for delivery toand deployment within a target blood vessel or other body lumen.Usually, the plurality of radially expansible rings will be arrangedalong an axial line, typically defined by a deployment balloon, adelivery tube, or some combination thereof. The expansible ring segmentswill be arranged so that the axially extending elements on each of thesegments is interleaved with corresponding axial extending elements onadjacent but unconnected ring segments. Referring now to FIGS. 1-4, sucharrangements will be generally described for both closed cell ringstructures (FIGS. 1 and 2) and open cell ring structures (FIGS. 3 and4).

[0046] In FIG. 1, a portion of a stent structure 10 comprising aplurality of radially expansible rings 12 is illustrated. Each radiallyexpansible ring 12 includes a plurality of closed rhomboid or diamondstructures 14 circumferentially joined by connectors 16. It willappreciated that the stent structure 10 is shown in a “rolled-out”configuration, and that only a portion of the structure is depicted forsimplicity. Usually, the stent structure would contain a greater numberof expansible rings 12, and each ring would include a larger number ofrhomboid cells.

[0047] Of particular importance to the present invention, FIG. 1illustrates that each rhomboid cell 14 includes an axially extendingelement 18 which interleaves with a similar element on an adjacent ringstructure. This interleaved structure permits a very close packing ofthe rings without the need to physically attach the rings. Moreover,when the stent structure is radially expanded, as shown in FIG. 2, theaxially extending elements 18 will usually continue to axiallyinterleave which increases the coverage of the body lumen wall beingtreated.

[0048] The advantages of the present invention are particularly apparentin curved blood vessels BV, as illustrated in FIGS. 2A and 2B. Anexpanded, non-interleaved multiple ring stent is shown in FIG. 2A.Substantial gaps G appear between the axially extending elements 18 onthe large diameter side of the curved vessel segment. In contrast, thenested stent configurations of the present invention are able tomaintain interleaving of the axially extending elements 18, even on thelarge diameter side of the curved vessel segment, as shown in FIG. 2B.While the present invention cannot assure that gaps will always beeliminated, the number and extent of the gaps will at least be reduced,thus improving wall coverage.

[0049] A similar result can be achieved with a stent structure 20comprising a plurality of open cell zigzag ring structures 22, shown inFIGS. 3 and 4. Each zigzag ring includes axially extending elementswhich alternate directions, and the rings are arranged so that theelements are “nested” as shown in FIG. 3. After radially expansion ofthe stent structure 20, the nested axially extending elements of therings 22 remain generally overlapping, as shown in FIG. 4, even when thestent has undergone significant radial expansion. While prior stentstructures have utilized nested zigzag structures, they have generallyeither connected adjacent structures or utilized only a single filamentfor forming such structures. In neither case can the flexibilityachieved by the present invention in combination with the ability toselectively deliver independent radially expansible segments beachieved.

[0050] Referring now to FIGS. 5-7, a particular stent structure 30comprising a plurality of radially expansible rings 32 is illustrated.Each ring 32, as shown in FIG. 5, comprises a plurality of closed cellboxes 34 joined at their midpoints by circumferentially directedconnectors 36. Each box 34 includes a central opening 35 which isgenerally an axial cut enlarged at each end and in the middle. As withprior illustrations, the ring structure 32 is shown in its rolled-out orflattened configurations. In the actual stent structure, the ring wouldbe rolled so that the “broken” connectors 34′ are in fact connected toform a cylindrical shape. The “bow tie” shape of the central opening 35is advantageous as it permits maximum radial compression of the stentwhile minimizing both the delivery profile and the stress relief of thestent during expansion in the body lumen.

[0051]FIG. 6 illustrates the very tight packing of the stent structure30 that can be achieved. The stent structure 30 in FIG. 6 is in itspre-deployment configuration as it would be when placed over a balloonor within a delivery tube, as described in more detail hereinbelow. Itcan be seen that virtually all of the available area for carrying thestent is covered. Thus, when the stent is expanded as shown in FIG. 7,the area of the blood vessel or other luminal wall will be maximized.Moreover, this very close packing of the stent is achieved whileconcurrently providing a very high degree of flexibility while the stentis being delivered and conformability after the stent is deployed. Suchflexibility results in large part from the fact that the adjacent ringsare unconnected and free to move relative to each other as the stent isdelivered and deployed. Coverage in curved vessels will be improved withthe specific design of FIGS. 6 and 7 generally as shown in FIGS. 2A and2B.

[0052] Axial separation of the rings 32 of stent structure 30 can beinhibited by modifying the ring geometries in a variety of ways, such asshown in FIGS. 6A and 6B. In FIG. 6A, the boxes 34 a are fabricated (ordeformed after fabrication) to collapse near the centers so that theyform “bow tie” structures, with enlarged ends 34 b interlocking.Alternatively, the boxes 34 c can be inclined relative to the axialdirection, as shown in FIG. 6B, to also provide interlocking of adjacentrings prior to deployment. Such inclination can be used with at leastmost of the embodiments of the present invention to improve axialretention. In addition, other patterns, such as chevrons, interleavedsigmoidal shapes, and the like could also be used to provide the desiredinterlocking prior to stent expansion.

[0053] Referring now to FIGS. 8-10, a similar degree of wall coverageand flexibility can be achieved with open cell stent structures. Stentstructure 40 (FIG. 9) comprises a plurality of open cell expansiblerings 42 formed in a “castellated” pattern, as shown in more detail inFIG. 8. The castellations comprise narrow U-shaped loops 44 and 46 whichalternatively extend in a right hand direction (loop 44) and left handdirection (loop 46) relative to a circumferential center line 48. Therings 42 are arranged so that the loops 44 and 46 overlap, as shown inFIG. 9, to form a tightly packed configuration. When expanded, as shownin FIG. 9, the loops 44 and 46 continue to overlap to provide a veryhigh degree of vessel wall coverage, as shown in FIG. 10. The open cellconfiguration of FIGS. 8-10 will also improve coverage in curvedvessels, minimizing gaps as discussed previously. The length of the opencells will be in the range from 0.5 to 10 mm, usually from 2 to 5 mm.

[0054] Referring now to FIGS. 11-14, additional embodiments of theradially expansible ring segments are illustrated. As with priorillustrations, the ring segments are shown in their pre-deployedconfiguration in a rolled-out manner. Ring structure 50 of FIG. 11comprises a plurality of closed cell box elements 52 joined bycircumferential connectors 54 and 56. Ring 50 is similar to ring 32 ofFIG. 5, except that the circumferential connectors 54 are split to formH-shaped slots 55 which span pairs of adjacent box structures 52 and theintermediate connectors 54 form a single, larger cell structures. Suchlarger openings are advantageous when stenting in blood vessels withside branches which must be kept open. In particular, the side branchesmay be accessed by opening the slots 55 with a balloon structure. Incontrast, the cell pattern of stent 32 (FIG. 5) provides a greatercoverage that may be of particular importance with drug eluting stents.

[0055] Stent structures comprising multiple rings 50 are shown in theirunexpanded and expanded configuration in FIGS. 1A and 11B, respectively.Of particular note, the open slots 55 (FIG. 11B) provide for significantadditional expansion (via balloon dilation or other subsequentintervention) in order to provide access to a side branch or for anyother purpose. A further expanded slot 55 is shown in FIG. 11C, asexpanded by balloon B.

[0056] Ring structure 60 of FIG. 12 comprises a plurality ofinterconnected box structures 62, 64, and 66. Each of the box structuresshares common axial struts or beams, but the axially offset nature ofthe three box structures permits radial expansion. Moreover, the boxstructures 62 and 66 provide the axially extending elements which may beinterleaved in forming a stent structure from a plurality of the rings60. Axially extending elements 62 and 66 interleave and mate so thatinterleaved extending elements of adjacent stents can be interferencefit with each other to provide a friction fit which inhibits separationof the stents, or be kept out of contact to allow for separation.Furthermore, extending elements can deflect radially inward which willprovide additional adherence to an expandable delivery balloon andincreased stent retention.

[0057] Ring structure 70 in FIG. 13 comprises paired, symmetric boxstructures 72 and 74 joined by short circumferential connectors 76. Eachof the box structures 72 and 74 define a long and a short axiallyextending member which can be aligned with each other when forming astent structure from a plurality of the rings 70. This particularstructure will provide good adherence to an expandable delivery balloonduring deployment and have many of the same advantages as the embodimentof FIG. 12.

[0058] Ring structure 80 of FIG. 14 is similar to that of ring structure70 of FIG. 13, except that the “longer” rings terminate in a retainer,such as T-ends 82. When deploying multiple rings 80 in a stentstructure, the T-ends will interlock to help hold the ring in place onthe balloon or within the delivery tube. The interlock, however, doesnot provide a permanent attachment and, adjacent ring segments 80 willnaturally release from each other during deployment. Moreover, since theinterlocking structures are not actually attached, they permit a highdegree of flexibility while the stent is being deployed. While T-endsare shown in FIG. 14, the terminal retainers could be L- or J-shapedends or have any other geometry, which also provides for interlocking.In particular, each of these geometries will include a peripherallyextending segment 83 which interlocks with a peripherally extendingsegment 83 on an adjacent T-end 82. Upon expansion of the ring 80, thesegment 83 will move apart allowing the adjacent rings to deployseparately. When deploying multiple rings 80 in a stent structure, theT-, L- or J-ends will interlock to help hold the ring in place on theballoon or within the delivery tube. The interlock, however, does notprovide a permanent attachment and, adjacent ring segments 80 willnaturally release from each other during deployment. Such interlockingcould also incorporated in the embodiments of FIGS. 5, 8, 11 and 12.

[0059] As illustrated thus far, the stent structures have generallymaximized to vessel wall coverage achieved after expansion. While thiswill often be desired, in some instances it may be desired to lessen theamount of wall coverage. The stent structures shown in FIGS. 15A and 15Band FIGS. 16A and 16B, achieve such reduced wall coverage by providing“spacers” between adjacent rings.

[0060] In FIG. 15A, a stent structure 90 includes independent rings 92having boxes 93 circumferentially separated by spacers 94. The spacers94 will either not expand or expand only after the boxes 93 haveexpanded, thus maintaining an axial distance D between adjacent ringsafter expansion, as shown in FIG. 15B. The distance D will be equal toabout one-half the total axial length of the spacer 94.

[0061] Stent structure 96 (FIGS. 16A and 16B) is similar to structure90, except that spaces 97 are axially split to define an H-shaped cell(as discussed with earlier embodiments) and certain of the rings 98 andjoined by sigmoidal links 99.

[0062] Stent structures according to the present invention may bedelivered in a variety of ways. As illustrated in FIGS. 17A-17C, thestent structure 30 may be delivered on a balloon catheter 90 having aballoon 92 with a single inflation chamber. Deployment of the stent 30is illustrated in FIG. 17B where all independent ring structures 32 areexpanded simultaneously. Alternatively, as illustrated in FIG. 17C,catheter may carry a balloon 94 having a plurality of independentlyinflatable compartments. In that way, one or more of the independentcompartments may be inflated separately from others of the compartmentsto selectively deploy one, two, three, or more of the independent ringstructures 32. In that case, others of the ring structures 32 willremain unexpanded and available for separate expansion or may be simplyremoved from the patient if unused.

[0063] Referring now to FIGS. 18A-18D, an alternative stent structuredelivery protocol employing a carrier tube will be described. Suchdelivery protocols are described in more detail in co-pendingapplication Ser. No. 10/306,813, filed on Nov. 27, 2002 (Attorney DocketNumber 021629-000320US), and in copending application Ser. No.10/637,713, filed Aug. 8, 2003 (Attorney Docket No. 21629-000340US), thefull disclosures of which are incorporated herein by reference. Catheter160 (FIG. 18A) comprises a sheath 164, pusher tube 166, and a catheterbody 168. The catheter body 168 includes an expansible balloon 170 overits distal portion. Individual expansible rings, as described above, aredeployed, as illustrated in FIGS. 18B and 18C, by first advancing thedistal-most ring 162 using the pusher tube 166. The catheter body 168 isalso distally advanced so that a distal portion of the balloon 170 lieswithin the distal-most deployed ring 162, as shown in FIG. 18B. Theremaining proximal portion of the balloon 170 will, of course, remainwithin the other rings 162 which themselves remain within the sheath164. The balloon 170 is then inflated, but only the advanced distalportion of the balloon inflates within the advanced ring 162, asillustrated in FIG. 18C. Expansion of the remaining proximal portion ofthe balloon is prevented by the sheath 164. Similarly, the remainingrings 162 remain unexpanded since they remain within the sheath 164.

[0064] Referring now to FIG. 18D, additional rings 162 may be deployed,either at the same target location within the blood vessel or at adifferent, spaced-apart locations within the blood vessel. Deployment oftwo rings 162 is illustrated. The two rings 162 are axially advancedusing the pusher tube 162 so that they are positioned over theuninflated balloon 170. The balloon 170 is then inflated, as illustratedin FIG. 18D, thus expanding the rings 162 within the blood vessel BV. Itwill be appreciated that the catheter 160 could carry many more than thefour illustrated rings 162, and three, four, five, ten, and even 20 ormore individual rings could be deployed at one time, with additionalsingle prostheses or groups of prostheses being deployed at differenttimes and/or at different locations within the blood vessel. The use of“stent valves” as described in application Ser. No. 10/306,813,previously incorporated herein by reference, may preferably be employedto facilitate controlling the number of rings deployed and the spacingbetween the deployed and undeployed rings.

[0065] Referring now to FIG. 13, kits 200 according to the presentinvention comprise a catheter 160 (or a balloon catheter) in combinationwith instructions for use IFU. The instructions for use set forth any ofthe methods of the present invention, and in particular set forth howthe catheter 160 may be used to implant a stent structure comprisingmultiple rings within a blood vessel or other body lumen. The catheter160 and instructions for use will typically be packaged together, forexample within a conventional package 202, such as a box, tube, pouch,tray, or the like. Catheter 160 will typically be maintained in asterile condition within the package 202. The instructions for use maybe provided on a package insert, may be printed in whole or in part onthe packaging, or may be provided in other ways, such as electronicallyover the internet, on an electronic medium, such as a CD, DVD, or thelike.

[0066] A further alternative stent structure according to the inventionis illustrated in FIGS. 20A-20B. FIG. 20A illustrates a portion of astent segment 201 in an unexpanded configuration, shown in a planarshape for clarity. Stent segment 201 comprises two parallel rows 203A,203B of I-shaped cells 205 formed around an axis A so that stent segment201 has a cylindrical shape. The terms “I-shaped” and “H-shaped” as usedherein may refer to a similar cell geometry comprising two generallyparallel slots connected by an interconnecting slot. Such cells mayappear H-shaped when axis A is in a vertical orientation, or I-shapedaxis A is in a horizontal orientation. Each cell 205 has upper and loweraxial slots 207 aligned with the axial direction and a circumferentialslot 204. Upper and lower slots 207 preferably have an oval, racetrack,rectangular or other oblong shape with a long dimension L generallyparallel to axis A and a short dimension W perpendicular thereto. Axialslots 207 are bounded by upper axial struts 206A and lower axial struts206B, curved outer ends 208 and curved inner ends 210. Eachcircumferential slot 204 is bounded by an outer circumferential strut209 and an inner circumferential strut 211. Each I-shaped cell 205 isconnected to the adjacent I-shaped cell 205 in the same row 98A or 98Bby a circumferential connecting strut 213. All or a portion of cells 205in row 98A merge or join with cells 205 in row 98B at the inner ends210, which are integrally formed with the inner ends 210 of the adjacentcells 205.

[0067] Stent segment 201 is configured to interleave with an adjacentstent segment of similar construction. Upper and lower axial struts206A, 206B and outer ends 208 form axial elements E that are received inthe spaces S between each element E of the adjacent stent segment 201.

[0068] In a preferred embodiment, a spacing member 212 extends outwardlyin the axial direction from a selected number of outer circumferentialstruts 209 and/or connecting struts 213. Spacing member 212 preferablyitself forms a subcell 214 in its interior, but alternatively may besolid without any cell or opening therein. For those spacing members 212attached to outer circumferential struts 209, subcell 214 preferablycommunicates with I-shaped cell 205. Spacing members 212 are configuredto engage the curved outer ends 208 of an adjacent stent segment 201 soas to maintain appropriate spacing between adjacent stent segments. Inone embodiment, spacing members 212 have outer ends 216 with twospaced-apart protrusions 218 that provide a cradle-like structure toindex and stabilize the curved outer end 208 of the adjacent stentsegment. Preferably, spacing members 212 have an axial length of atleast about 10%, more preferably at least about 25%, of the longdimension L of I-shaped cells 205, so that the I-shaped cells 205 ofadjacent stent segments are spaced apart at least that distance. Thisresults in elements E interleaving a distance of at least about 10%,preferably at least about 25%, and more preferably at least about 50% oftheir axial length as measured from the circumferential connectingstruts 213. Because spacing members 212 experience little or no axialshortening during expansion of stent segments 201, this minimum spacingbetween stent segments is maintained both in the unexpanded and expandedconfigurations.

[0069]FIG. 20B shows stent segment 201 of FIG. 20A in an expandedconfiguration. It may be seen that cells 205 are expanded so that upperand lower slots 207 are diamond shaped with circumferential slots 204remaining basically unchanged. This results in some axial shortening ofthe stent segment, thereby increasing the spacing between adjacent stentsegments. The stent geometry is optimized by balancing the amount ofaxial shortening and associated inter-segment spacing, the desireddegree of vessel wall coverage, the desired metal density, and otherfactors. Because the stent is comprised of multiple unconnected stentsegments 201, any desired number from 2 up to 10 or more stent segmentsmay be deployed simultaneously to treat lesions of any length from 2 mmup to 100 mm or more. Further, because such segments are unconnected toeach other, the deployed stent structure is highly flexible and capableof deployment in long lesions having curves and other complex shapes.

[0070] As an additional feature, circumferential slots 204 provide apathway through which vessel side branches can be accessed for catheterinterventions. Should stent segment 201 be deployed at a location inwhich it covers the ostium of a side branch to which access is desired,a balloon dilatation catheter may be positioned through circumferentialslot 204 and expanded. This deforms circumferential struts 209, 211axially outward, thereby expanding circumferential slot 204 and furtherexpanding upper and lower slots 207, as shown in phantom in FIG. 20B.This provides a relatively large opening 220 through which a cathetermay be inserted through stent segment 201 and into the side branch forplacing stents, performing angioplasty, or carrying out otherinterventions.

[0071]FIGS. 21A-21B illustrate a second embodiment of a stent segment201′ according to the invention. In FIG. 21A, two stent segments 201′are shown interleaved in a planar shape for clarity. Similar to theembodiment of FIG. 20A, stent segment 201′ comprises two parallel rows222A, 222B of I-shaped cells 224 formed into a cylindrical shape aroundaxial axis A. Cells 224 have upper and lower axial slots 226 and aconnecting circumferential slot 228. Upper and lower axial slots 226 arebounded by upper axial struts 230, lower axial struts 232, curved outerends 234, and curved inner ends 236, forming axial elements E configuredto be received in spaces S between elements E in the adjacent stentsegment 201′. Circumferential slots 228 are bounded by an outercircumferential strut 238 and inner circumferential strut 240. EachI-shaped cell 224 is connected to the adjacent I-shaped cell 224 in thesame row 222 by a circumferential connecting strut 242. Row 222A isconnected to row 222B by the merger or joining of curved inner ends 236of at least one and preferably two of slots 226 in each row 222.

[0072] One of the differences between the embodiment of FIGS. 21A-21Band that of FIGS. 20A-20B is the way in which spacing is maintainedbetween the adjacent interleaved stent segments. In place of the spacingmembers 212 of the earlier embodiment, the embodiment of FIG. 21Aincludes a bulge 244 in upper and lower axial struts 230, 232 extendingcircumferentially outwardly from axial slots 226. These give axial slots226 an arrowhead or cross shape at their inner and outer ends. The bulge244 in each upper axial strut 230 extends toward the bulge 244 in alower axial strut 232 in the same cell 205 or in an adjacent cell 205,thus narrowing the space S therebetween and creating a concave abutment246 in the space between each axial slot 226. Concave abutments 246 areconfigured to receive and engage curved outer ends 234 of cells 224 inthe adjacent stent segment, thereby maintaining spacing between thestent segments. The axial location of bulges 244 along upper and loweraxial struts 230, 232 may be selected to provide the desired degree ofinter-segment spacing. Preferably, the axial depth of concave abutments246 from curved outer ends 234 is at least about 10% of the axial lengthof elements E (measured from circumferential struts 242), preferably atleast about 25% of the axial length of elements E, and more preferablyat least about 50% of the axial length of elements E.

[0073]FIG. 21B shows two stent segments 201 of FIG. 21A in an expandedcondition. It may be seen that axial slots 226 are deformed into acircumferentially-widened modified diamond shape with bulges 244 on thenow diagonal upper and lower axial struts 230, 232. Circumferentialslots 228 are generally the same size and shape as in the unexpandedconfiguration. Bulges 244 have been pulled away from each other to someextent, but still provide a concave abutment 246 to maintain a minimumdegree of spacing between adjacent stent segments. As in the earlierembodiment, some axial shortening of each segment occurs upon expansionand stent geometry can be optimized to provide the ideal intersegmentspacing.

[0074] In a preferred embodiment, stent segments 201′ retain some degreeof interleaving in the expanded configuration, with outer ends 234 ofelements E on adjacent stent segments being at least circumferentiallyaligned with each other, and preferably extending into spaces S of theadjacent stent segment a distance of at least about 1%, more preferablyat least about 5%, and in some cases at least about 10% of the axiallength of elements E as measured from circumferential connecting struts242. In one exemplary embodiment, for a stent segment 201′ having anaxial length of 4 mm and an unexpanded diameter of about 0.5-1.5 mm,elements E have an axial length of about 1 mm and are interleaved adistance D_(u) of about 0.1-0.5 mm in the unexpanded configuration.Segments 201′ are expandable to a diameter of 2.5-3.5 mm and elements Eare interleaved a distance De of about 0.01-0.1 mm in the expandedconfiguration.

[0075] It should also be noted that the embodiment of FIGS. 21A-21Bretains the feature described above with respect to FIGS. 20A-20B toenable access to vessel side branches blocked by stent segment 201′.Should such side branch access be desired, a dilatation catheter may beinserted into circumferential slot 228 and expanded to provide anenlarged opening through which a side branch may be entered.

[0076]FIGS. 22A-22B illustrate a variant of the stent structure of FIGS.21A-21B that has a larger expanded diameter. The primary difference inthe embodiment of FIGS. 22A-22B is the geometry of the inner ends 236′of each axial slot 226′. Rather than being curved, inner ends 236′ aregenerally straight and oriented in the circumferential direction.Because of the longer circumferential dimension of the inner ends 236′,an inner portion 250 of each axial strut 230′, 232′ is disposed at anangle relative to the axial direction, giving the inner half 252 of eachaxial slot 226′a trapezoidal shape. Again, bulges 244′ are disposedalong axial struts 230′, 232′ so as to create concave abutments 246′that engage the outer ends 234′ of axial slots 226′ and maintaininter-segment spacing.

[0077] As shown in FIG. 22B, stent segment 201″ expands to aconfiguration similar to that of FIG. 21B, with the exception that innerends 236′ remain generally straight and aligned with the circumferentialdirection. Axial slots 226′ are again expanded into a modified diamondshape, with bulges 244′ extending into spaces S to maintaininter-segment spacing. In an exemplary embodiment, stent segment 201″has a length of about 4 mm and diameter of about 1.0-2.0 mm whenunexpanded, and is expandable to a diameter of about 3.0-4.0 mm.

[0078] The stent structures of the invention are preferably radiopaqueso as to be visible by means of fluoroscopy. Radiopaque markers and/ormaterials may be used in or on the stent structures. Markers ofradiopaque materials may be applied to the exterior of the stents, e.g,by applying a metal such as gold, platinum, a radiopaque polymer, orother suitable coating or mark on all or a portion of the stents.Alternatively, the stent structures may include a radiopaque cladding orcoating or may be composed of radiopaque materials such as MP35N (ASTM562), L-605 cobalt chromium (ASTM F90), other suitable alloys containingradiopaque elements, or multilayered materials having radiopaque layers.As a further option, the stent structures may have a geometry conduciveto fluoroscopic visualization, such as having struts of greaterthickness, sections of higher density, or overlapping struts. Some ofthe possible materials that may be used in the stent segments, eitheralone or in combination, include (by ASTM number):

[0079] F67-00 Unalloyed Titanium

[0080] F75-01 Cobalt-28 Chromium-6 Molybdenum Alloy

[0081] F90-01 Wrought Cobalt-20 Chromium-15 Tungsten-10 Nickel Alloy

[0082] F136-02a Wrought Titanium-6 Aluminum-4 Vanadium ELI Alloy

[0083] F138-00, F139-00 Wrought 18 Chromium-14 Nickel-2.5 MolybdenumStainless Steel Bar or Sheet

[0084] F560-98 Unalloyed Tantalum

[0085] F562-02 Wrought 35 Cobalt-35 Nickel-20 Chromium-10 MolybdenumAlloy

[0086] F563-00 Wrought Cobalt-20 Nickel-20 Chromium 3.5 Molybdenum-3.5Tungste-5 Iron Alloy

[0087] F688 Wrought Cobalt-35 Nickel-20 Chromium-10 Molybdenum Alloy

[0088] F745-00 18 Chromium-12.5 Nickel-2.5 Molybdenum Stainless Steel

[0089] F799-02 Cobalt-28 Chromium-6 Molybdenum Alloy

[0090] F961-96 Cobalt-35 Nickel-20 Chromium-10 Molybdenum Alloy

[0091] F1058-02 Wrought 40 Cobalt-20 Chromium-16 Iron-15 Nickel-7Molybdenum Alloy

[0092] F1091-02 Wrought Cobalt-20 Chromium-15 Tungsten-10 Nickel Alloy

[0093] F1108 Titanium-6 Aluminum-4 Vanadium Alloy

[0094] F1295-01 Wrought Titanium-6 Aluminum-7 Niobium Alloy

[0095] F1314-01 Wrought Nitrogen-strengthened 22 Chromium-13 Nickel-5Manganese-2.5 Molybdenum Stainless Steel Alloy

[0096] F1241-99 Unalloyed Titanium Wire

[0097] F1350-02 Wrought 18 Chromium-14 Nickel-2.5 Molybdenum StainlessSteel Wire

[0098] F1377-98a Cobalt-28 Chromium-6 Molybdenum Powder coating

[0099] F1472-02 a Wrought Titanium-6 Aluminum-4 Vanadium Alloy

[0100] F1537-00 Wrought Cobalt-28 Chromium-6 Molybdenum Alloy

[0101] F1580-01 Titanium and Titanium-6 Aluminum-4 Vanadium Alloy Powdercoating

[0102] F1586-02 Wrought Nitrogen Strengthened 21 Chromium-10 Nickel-3Mnaganese-2.5 Molybdenum Stainless Steel Bar

[0103] F1713-96 Wrought Titanium-13 Niobium-13 Zirconium Alloy

[0104] F1813-01 Wrought Titanium-12 Molybdenum-6 Zirconium-2 Iron Alloy

[0105] F2063-00 Wrought Nickel-Titanium Shape Memory Alloys

[0106] F2066-01 Wrought Titanium-15 Molybdenum Alloy

[0107] F2146-01 Wrought Titanium-3 Aluminum-2.5 Vanadium Alloy SeamlessTubing

[0108] F2181-02a Wrought Stainless Steel Tubing

[0109] The preferred embodiments of the invention are described above indetail for the purpose of setting forth a complete disclosure and forthe sake of explanation and clarity. Those skilled in the art willenvision other modifications within the scope and sprit of the presentdisclosure.

What is claimed is:
 1. A stent structure comprising: a plurality ofradially expansible rings arranged along an axial line, wherein at leastsome of the axially adjacent rings are not connected and wherein atleast some of the axially unconnected rings comprise axially extendingelements which interleave with axially extending elements on an adjacentunconnected ring without interlocking with the adjacent unconnectedring.
 2. A stent structure as in claim 1, wherein at least some of theaxially extending elements comprise expansible closed structures whichopen as the rings are expanded.
 3. A stent structure as in claim 2,wherein the expansible closed structures are selected from the groupconsisting of boxes, diamonds, rhomboids, ovals, and ellipses.
 4. Astent structure as in claim 2, wherein the closed cells are defined by aslot pattern selected from the group consisting of I-patterns,H-patterns, and J-patterns.
 5. A stent structure as in claim 1, whereinat least some of the axially extending elements comprise expansible openstructures.
 6. A stent structure as in claim 5, wherein the expansibleopen structures are selected from the group consisting of serpentinestructures, zigzag structures, and castellated structures.
 7. A stentstructure as in claim 1, wherein at least some of the axiallyunconnected rings further comprise spacers which engage the axiallyextending elements on adjacent rings to provide a preselected spacingbetween adjacent rings upon radial expansion.
 8. A stent structure as inclaim 1, wherein the axially unconnected rings are configured to axiallyshorten upon expansion.
 9. A stent structure as in claim 1, wherein theaxially extending elements remain interleaved following expansion.
 10. Astent structure as in claim 1, wherein the axially extending elementsaxially interleave over a distance of at least 0.1 mm prior to stentexpansion.
 11. A stent structure as in claim 10, wherein the distance isin the range from 1 mm to 5 mm.
 12. A stent structure as in claim 1,wherein the rings have axial lengths in range from 1 mm to 10 mm, priorto radial expansion.
 13. A stent structure as in claim 1, consisting offrom two to 50 expansible ring structures.
 14. A stent structure as inclaim 1, wherein the radially expansible rings releasably carry abiologically active agent.
 15. A stent structure as in claim 14, whereinthe biologically active agent inhibits hyperplasia.
 16. A stentstructure as in claim 15, wherein the biologically active agent isselected from the group consisting of anti-neoplastic drugs, includingpaclitaxel, methotrexate, and batimastal; antibiotics includingdoxycycline, tetracycline, rapamycin, and actinomycin;immunosuppressants including dexamethasone, and methyl prednisolone;nitric oxide sources including nitroprussides; estrogen; and estradiols.17. A stent deployment system comprising: an elongated carrier having acentral axis; a plurality of radially expansible rings arranged over asurface of the elongated carrier, wherein at least some of the radiallyexpansible rings comprise axially extending elements which interleavewith axially extending elements on an adjacent unconnected ring withoutinterlocking with the adjacent radially expansible ring.
 18. A stentdeployment system as in claim 17, wherein the elongated carriercomprises a radially expansible balloon having an outer surface, whereinthe radially expansible rings are disposed over the outer surface of theballoon.
 19. A stent deployment system as in claim 18, wherein theballoon consists of a single inflation chamber.
 20. A stent deploymentsystem as in claim 18, wherein the balloon comprises a plurality ofindependent chambers wherein individual expansible rings are disposedover single independently inflatable chambers.
 21. A stent deploymentsystem as in claim 17, wherein the elongated carrier comprises a carriertube having an inner surface which constrains the radially expansiblerings.
 22. A stent deployment system as in claim 21, further comprisinga pusher tube arranged to axially advance the radially expansible ringsfrom the carrier tube.
 23. A stent deployment system as in claim 22,wherein the radially expansible rings are resilient and radiallyconstrained so that they expand when advanced distally from the carriertube.
 24. A stent deployment system as in claim 17, wherein the radiallyexpansible rings are deformable, said structure further comprising aballoon arranged to expand individual rings as said rings are advancedfrom the carrier tube.
 25. A stent deployment system as in claim 17,wherein at least some of the axially expanding elements compriseexpansible closed structures.
 26. A stent deployment system as in claim25, wherein the expansible closed structures are selected from the groupconsisting of boxes, rhomboids, ovals, ellipses, diamonds, and irregularpolygons.
 27. A stent deployment structure as in claim 25, wherein theclosed cells are defined by a slot pattern selected from the groupconsisting of I-patterns and H-patterns.
 28. A stent deploymentstructure as in claim 17, wherein at least some of the axiallyunconnected rings further comprise spacers which engage the axiallyextending elements on adjacent rings to provide a preselected spacingbetween adjacent rings upon radial expansion.
 29. A stent deploymentsystem as in claim 17, wherein at least some of the axially extendingelements comprise expansible open structures.
 30. A stent deploymentsystem as in claim 29, wherein the expansible open structures areselected from the group consisting of expansible structures, zigzagstructures, and castellated structures.
 31. A stent deployment structureas in claim 17, wherein the radially expansible rings are configured toaxially shorten upon expansion.
 32. A stent deployment structure as inclaim 17, wherein the axially extending elements remain interleavedfollowing expansion.
 33. A stent deployment structure as in claim 17,wherein the axially extending elements axially interleave over adistance of at least 0.1 mm prior to stent expansion.
 34. A stentdeployment structure as in claim 33, wherein the distance is in therange from 1 mm to 5 mm.
 35. A stent deployment system as in claim 17,wherein the rings have axial lengths in range from 11 mm to 10 mm, priorto radial expansion.
 36. A stent deployment system as in claim 35,consisting of from two to 50 expansible ring structures.
 37. A stentdeployment system as in claim 17, wherein the radially expansible ringsreleasably carry a biologically active agent.
 38. A stent deploymentsystem as in claim 37, wherein the biologically active agent inhibitshyperplasia.
 39. A stent deployment system as in claim 38, wherein thebiologically active agent is selected from the group consisting ofanti-neoplastic drugs including paclitaxel, methotrexate, andbatimastal; antibiotics including doxycycline, tetracycline, rapamycin,and actinomycin; immunosuppressants including dexamethasone and methylprednisolone; nitric oxide sources including nitroprussides; estrogen;and estradiols.
 40. A method for arranging multiple independent stentrings on a carrier of a catheter, said method comprising: providing anelongated carrier structure; mounting a plurality of radially expansiblerings comprising axially extending elements on the carrier structure,wherein the axially extending elements on adjacent rings interleave whenmounted on the carrier structure without interlocking.
 41. A method asin claim 40, wherein the number of rings mounted on the carrierstructure is selected to provide a desired overall stent length.
 42. Amethod as in claim 41, wherein the number of rings is from two to 50 andthe overall stent length is in the range from 2 mm to 200 mm.
 43. Amethod as in claim 40, wherein at least some of the axially extendingelements comprise expansible closed structures.
 44. A method as in claim43, wherein the expansible closed structures are selected from the groupconsisting of boxes, rhomboids, ovals, ellipses, diamonds, and irregularpolygons.
 45. A method as in claim 43, wherein the expansible closedstructures are defined by a slot pattern selected from the groupconsisting of I-patterns and H-patterns, and J-patterns.
 46. A method asin claim 40, wherein at least some of the axially extending elementscomprise expansible open structures.
 47. A method as in claim 46,wherein the expansible open structures are selected from the groupconsisting of serpentine structures, zigzag structures, and castellatedstructures.
 48. A method as in claim 40, wherein at least some of theaxially unconnected rings further comprise spacers which engage theaxially extending elements on adjacent rings to provide a preselectedspacing between adjacent rings upon radial expansion.
 49. A method as inclaim 40, wherein the radially expansible rings are configured toaxially shorten upon expansion.
 50. A method as in claim 40, wherein theaxially extending elements remain interleaved following expansion.
 51. Amethod as in claim 40, wherein the axially extending elements axiallyinterleave over a distance of at least 0.1 mm prior to stent expansion.52. A method as in claim 51, wherein the distance is in the range from 1mm to 5 mm.
 53. A method as in claim 40, wherein the rings have axiallengths in range from 1 mm to 10 mm, prior to radial expansion.
 54. Amethod as in claim 53, wherein the rings have axial lengths in the rangefrom 0.9 mm to 9 mm after radial expansion.
 55. A method as in claim 54,consisting of from two to 50 expansible ring structures.
 56. A method asin claim 40, wherein the radially expansible rings releasably carry abiologically active agent.
 57. A method as in claim 56, wherein thebiologically active agent inhibits hyperplasia.
 58. A method as in claim57, wherein the biologically active agent is selected from the groupconsisting of anti-neoplastic drugs including paclitaxel, methotrexateand batimastal; antibiotics including doxycycline, tetracycline,rapamycin, and actinomycin; immunosuppressants including dexamethasoneand methyl prednisolone; nitric oxide sources including nitroprussides;estrogen; and estradiols.
 59. A method for stenting a body lumen, saidmethod comprising: delivering to the body lumen a stent structure havinga plurality of radially expansible rings arranged along an axial line,wherein at least some of the axially adjacent rings are not connectedand wherein at least some of the axially unconnected rings compriseaxially extending elements which interleave with axially extendingelements on an adjacent unconnected ring without interlocking with theadjacent unconnected ring; and expanding at least some of the ringswithin the body lumen so that the axially extending elements open andaxially move apart from each other.
 60. A method as in claim 59, whereinthe body lumen is a blood vessel.
 61. A method as in claim 60, whereinthe blood vessel is an artery.
 62. A method as in claim 59, wherein twoto 50 rings are delivered over a luminal length in the range from 2 mmto 200 mm.
 63. A method as in claim 59, wherein at least some of theaxially extending elements comprise expansible closed structures whichcircumferentially expand as the rings are expanded.
 64. A method as inclaim 63, wherein the expansible closed structures are selected from thegroup consisting of boxes, rhomboids, ovals, ellipses, diamonds, andirregular polygons.
 65. A method as in claim 63, wherein the closedcells are defined by a slot pattern selected from the group consistingof I-patterns, H-patterns, and J-patterns.
 66. A method as in claim 59,wherein at least some of the axially extending elements compriseexpansible open structures which circumferentially expand as the ringsare expanded.
 67. A method as in claim 66, wherein the expansible openstructures are selected from the group consisting of serpentinestructure, zigzag structures, and castellated structures.
 68. A methodas in claim 59, wherein at least some of the axially unconnected ringsfurther comprise spacers which engage the axially extending elements onadjacent rings to provide a preselected spacing between adjacent ringsupon radial expansion.
 69. A method as in claim 59, wherein the axiallyextending elements remain interleaved following expansion.
 70. A methodas in claim 59 wherein the radially expansible rings are configured toaxially shorten upon expansion.
 71. A method as in claim 59, wherein theaxially extending elements axially interleave over a distance of atleast 0.1 mm prior to stent expansion.
 72. A method as in claim 71,wherein the distance is in the range from 1 mm to 5 mm.
 73. A method asin claim 59, wherein the radially expansible rings carry a biologicallyactive agent which is released in the body lumen after the rings areexpanded.
 74. A method as in claim 73, wherein the biologically activeagent inhibits hyperplasia.
 75. A method as in claim 74, wherein thebiologically active agent is selected from the group consisting ofanti-neoplastic drugs including paclitaxel, methotrexate and batimastal;antibiotics including doxycycline, tetracycline, rapamycin, andactinomycin; immunosuppressants including dexamethasone and methylprednisolone; nitric oxide sources including nitroprussides; estrogen;and estradiols.
 76. A method as in claim 59, wherein the body lumen iscurved, and wherein the axially extending members remain interleavedafter expansion of the stent is performed.